A 604's XO point is well above the cab's 'sphere of influence', so has no bearing on its design/performance. The baffle area OTOH affects baffle step diffraction requirements [if any], but as long as the XO is adjustable it can usually be dialed in. Worst case, additional series resistance may be required if a very narrow baffle is used, so the rule-of-thumb is to maintain the same [or larger] baffle width as the cab the speaker was 'voiced' in.

GM